Add basic event handlers to game module

game.ex

@spec handle_event(String.t(), map(), Socket.t()) :: {:noreply, Socket.t()} | {:stop, Socket.t()}
def handle_event("keydown", payload, socket) do
  IO.puts("Received keydown event")
  IO.inspect(payload, label: "Payload for keydown")

  {:noreply, socket}
end

def handle_event("keyup", payload, socket) do
  IO.puts("Received keyup event")
  IO.inspect(payload, label: "Payload for keyup")

  {:noreply, socket}
end